Refining process for removing Mo from high-Ni and/or high-Co, Mo-containing alloy steels

ABSTRACT

High-Ni and/or high-Co, Mo-containing alloy steel is melted and peroxidized to convert Mo contained in the steel into molten Mo oxides. This peroxidized molten steel is treated with a molten slag forming agent comprising at least one basic oxide selected from the group consisting of alkali metal oxides and alkaline earth metal oxides and at least one acid oxide, to form double salts with the said Mo oxides and the said slag forming agent, and then discharging steel slag containing the said double salts.

Matted States Patent [1 1 Nagnro et at.

[ REFHNHNG PROCESS FOR REMOVING MO FROM HIGH-Nil AND/0R HIGH-CO,MiG-CONTAINING ALLOY STEELS [75] Inventors: Kazutalta Naguro; TaltaoSeya, both of Tokyo, Japan [73] Assignee: Kawaguchi Seiko KabushikiKaisha, Kawaguchi, Japan [22] Filed: Sept. 17, 1973 [21] Appl. No.:398,157

[30] Foreign Application Priority Data Mar. 23, 1973 Japan 48-32736 [52]U.S. Cl... 75/53, 75/54, 75/55,

7 75/129 [51] Int. Cl. C2lc 7/04, C22c 33/00 [58] Field of Search75/53-60, 129

[56] 1 References Cited UNITED STATES PATENTS r 3,309,196 3/1967 Kaneko75/53 [4 Feb. 18, 1975 1/1966 Richter .[75/60 5/1967 Bowden ..75/53Primary Examiner- Peter D. Rosenberg Attorney/432m, or FirmFlynn &Frishauf 5 7] ABSTRACT 5 Claims, N0 Drawings 1 REFINING PROCESS FORREMOVING MO FROM HIGH-NI AND/OR HIGH-CO, MO CONTAINING ALLOY STEELSFIELD OF THE INVENTION This invention has to do with the refining ofmolybdenum-containingalloy steels to remove molybdenum (Mo) therefrom.

BACKGROUND OF THE INVENTION In the past, it has been very difficult toeliminate Mo from high-Ni and/or high-Co, Mo-containing alloy steelsused particularly in jet engines and gas turbines. Mo has a considerablylower oxygen-affinity than has Fe. Mo oxides have less stability thanFeO and larger dissociation constants than FeO, such that M is notpractically oxidized in an oxidation refining in which undesirableelements are removed in the form of slag by oxidation.

In spite of these reasons, we have long carried out research on a methodfor facilitating the transfer of the Mo oxides into slag, based on ourrecognition that M0 is still present in molten steel in the form of Mooxides in combination with oxygen, though in a slight quantity in moltensteel in the peroxidized state, and the further recognition that the Mooxides have a very low solubility and exhibit very slight transfer intoslag in an ordinary oxidation refining. As a result, we have discoveredthat Mo oxides dissolved in molten steel can be transferred into slag bycombination with a molten basic slag forming agent comprising at leastone basic oxide se lected from the group consisting of alkali metaloxides and alkaline earth metal oxides and at least one acid oxide asprincipal constituents.

The object of this invention is to provide a refining process foreffectively removing Mo from high-Ni, and- /or high-Co, Mo-containingalloy steels.

SUMMARY OF THE INVENTION In accordance with the present invention, thereis provided a process for subjecting a high-Ni, and/or high-Co,Mo-containing alloy steel to oxidation melting refining to form aperoxidized molten steel containing Mo oxides; contacting theperoxidized molten steel with a basic double oxide, comprising (i) atleast one basic oxide selected from the group consisting of an alkalimetal oxide and an alkaline earth metal oxide and (ii) at least one acidoxide, and with at least one oxidizer selected from the group consistingof a solid oxidizer, oxygen gas, an oxygen-enriched gas and a mixturethereof, toform a double salt of said double oxide and said Mo oxides;and discharging a slag containing said double salt.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a more detailed descriptionof the present invention, a high-Ni and/or high-Co, Mo-containing alloysteel is melted, the said molten steel is subjected to oxidationrefining by means of a solid oxidizer such as iron ore or a gaseousoxidizer such as oxygen gas, and substantial amounts of Cr, C, P, Mn, Siand other undesirable elements contained in the said molten steel areremoved. When thisoxidation refining is excessive, the

said molten steel is partially peroxidized, thus resulting in thepartial oxidation of the Mo constituent and transfer of Mo into slag.Because the amount of this transfer is very slight, and there is aconsiderable oxidation loss of Fe and other alloying elements, theMo-removing refining, if conducted during this oxidation refining, wouldhave only a limited effect. If most of the C, P, Mn and Si constituentswere oxidized, it would be possible to cause the transfer of Mo inmolten steel into slag even in the presence of a considerable amount ofCr. However, it has been revealed experimentally that the Mo-removingreactions proceeded fully only when the Cr content in'the molten steelis decreased to less than about 1 percent by weight, the contents ofeach of C, P, Mn and Si are decreased to less than about 0.1 percent byweight, respectively, and the oxidation r'efining is applied to a moltensteel containing more than about 0.02 percent by weight of oxygen.

The said Mo-removing reactions are carried out through the addition ofoxidizers and a basic double oxide into molten steel at the same time.The said oxidizers include such solid oxidizers as Fe O FeO and Fe O andsuch gaseous oxidizersinclude oxygen, air, and oxygen-enriched gases.The said basic double oxide, which has previously been melted andcombined and exhibits basicity as a whole, is principally composed ofone or more basic oxides selected from the group consisting of alkalimetal oxides and alkaline earth metal oxides such as Na O, CaO, MgO, K0, Li O, BeO, BaO, SrO, Cs O and mixtures of two or more thereof, and atleast one acid oxide selected from SiO A1 0 and mixtures thereof. Thus,the basic double oxides are typified by: 2Na O.SiO 2CaO.SiO 3K O.Al O3CaO.2Al O and 3MgO.SiO

Accordingly as the said Mo-removing reactions proceed, leading to alower content of M0 in molten steel, the content of Mo oxides in slagformed by Moremoving refining becomes higher, and this makes furtherMo-removing reactions difficult to take place under the effect of Moequilibrium between slag and molten steel. It is therefore necessary torepeat Moremoving refining several times to exclude slag and to form newslag. The frequency of this Mo-removing refining varies with the levelof Mo-removaland the degree of operational success; two or three cyclessuffice when reducing the Mo content to less than 0.05 percent frommolten steel containing 2 percent M0.

The said Mo-removing reactions depend upon the molten steel temperature,degree of peroxidation and the presence of alloy elements. Lowtemperatures have in general a desirable effect on such reactions, andthe oxygen activity of alloy elements exerts an influence on thesereactions. Mose of the alkali metals and alkaline earth metals have avery high affinity for oxygen as compared with that of Fe, Ni and Co,and are therefore hardly contained as alloy elements in molten steel byreduction, even when their oxides are added or injected into moltensteel, but these alkali metal oxides and alkaline earth metal oxides arepresent in slag in a stable state in combination with Mo oxides. Thesaid basic oxides include Na O, CaO, MgO, K 0, LiO BeO, BaO, SrO andCsO, and the said acid oxides include SiO and A1 0 As described above, byadding or directly injecting into peroxidized molten steel thepreviously melted and cooled double slag forming agent consistingprincipally of alkali metal oxides and/or alkaline earth metal oxidesand acid oxides, the Mo constituent in the said molten steel issubjected to Mo-removing refining through its conversion into slag inthe form of double salts in combination of the said molten double slagforming agent and Mo oxides.

The following examples will illustrate the practical application of thepresent invention. All percentages mentioned below are by weight unlessotherwise indicated.

EXAMPLE 1 1. Melting-down:

2. Oxidation melting refining:

After slagging, 25kg of CaO and 200kg of iron ore were added into thesaid melt-down molten steel for a cycle, and Cr-removing oxidationrefining was conducted while blowing oxygen into the resulting moltenmixture. This cycle of oxidation melting operation involving adding CaOand iron ore while blowing oxygen and slagging, was repeated eighttimes. Consequently, a molten steel containing 0.1 percent Cr and 1.24percent Mo was formed.

3. Mo-removing refining:

Then, Na 'O and SiO were mixed at a mol ratio of 2:1, melted,and aftercooling, milled to a particle diameter of 1 -2mm, thus forming a slagforming agent comprising basic double oxides of the present invention.Mo-removing refining was performed by adding 80kg of this slag formingagent and 30kg of iron ore for every cycle into molten steel after theoxidation melting refining. During this Mo-removing refining, there wereno fumes, and the Mo content in molten steel was decreased to 0.062percent through four-cycles of this refining. The molten steel obtainedhad a chemical analysis of 22.9 percent Ni, 21.9 percent Co, 0.062percent Mo, 0.012 percent C, 0.012 percent P, traces of each of Cr, Siand Mn, and the balance Fe.

For comparison, Mo-removing refining was carried out by adding 80kg ofNa CO and 30kg of iron ore per cycle to molten steel after the saidoxidation melting. White fumes were evolved. The fumes principallycomprised decomposed CO gas and Na O evaporating at about 1,250C.Furthermore, in order to reduce the Mo content in molten steel to theabove presented level of 0.062 percent, it was required to repeat thecycle six times, and the furnace wall was seriously damaged.

EXAMPLE 2 ple 1, principally consisting of 2CaO.SiO- in the form 6 of adouble oxide powder was injected, with high pressure air as carrier gas,into the said peroxidized molten steel. This constituted the first cycleof Mo-removing refining. There was almost no white fume which mightcause air pollution, during injection. After the completion of the saidfirst cycle of injection, slag was discharged, and a second injectionwas conducted in the same manner. Upon the completion of a third similarinjection, the Mo content in molten steel decreased to 0.052 percent,and the molten steel had a chemical analysis comprising 23.9 percent Ni,22.3 percent Co, 0.05 percent Mo, 0.014 percent C, trace of Cr, and thebalance substantially Fe.

For comparison, another Mo-removing operation was carried out under thesame conditions as in the operation presented above, except for the useof lime (CaO) powder in place of 2CaO.SiO powder. White fumes wereproduced during the injection operation, and five cycles of injectionand slagging were required for reducing the Mo content in molten steelto about 0.05 percent.

As is clearly shown in Examples 1 and 2, the slag forming agent showingthe basici'ty in the present invention is formed by admixture and thenmelted. ln adding and injecting this slag forming agent into a moltensteel, therefore, no toxic gas is produced, thus leading to no pollutionnor damage to the furnace wall. Furthermore, as the slag forming agentof this invention is formed with a a previously melted and cooled doublesalt made from basic oxides and acid oxides, it is rapidly stabilizedafter its addition into molten steel in the form of a molten slag layer.

This invention is applicable vto all high-Ni and/or high-Co,Mo-containing alloy steels containing about 20 percent by weight or moreNi and/or Co in total.

Oxidation melting refining of high Ni and/or high- Co, Mo-containingalloy steel is repeated until, in the peroxidized molten steels thusobtained, the C content becomes less than about 1 percent by weight, thecontents of each of C, P and Mn, less than about 0.1 percent by weight,and the 0 content, more than about 0.02 percent by weight.

In the oxidation melting refining of the' Mocontaining alloy steels,temperatures of from about 1,500 C. to about 1,650 C. are generallyemployed. The Mo-containing alloy steels are peroxidized to an oxygencontent of from about 0.02 to about 0.3 percent by weight of oxygen.Thus, the peroxidized molten steel is at a temperature of from about1,400 C. to about 1,550 C. when contacted with the basic double oxideand an oxidizer.

The quantity of basic double oxide employed can be varied considerably.Generally, from about 50 to about 60 kilograms of double oxide are usedfor each ton of Mo-containing alloysteel. Similarly, from about 0.5m toabout 2m of oxygen as an oxidizer are used for each ton of Mo-containingalloy steel.

What is claimed is:

l. A refining process for removing Mo from a Mocontaining alloy steelhaving a high content of at least one of Ni and Co, which comprises:

subjecting said Mo-containing alloy steel to oxidation melting refiningat a temperature of from about 1500".C. to about l650C. to form aperoxidized molten steel containing Mo oxides and having the followingapproximate elemental analysis in percent contacting said peroxidizedmolten steel at a temperature of from about l400C. to about 1550C. witha basic double oxide comprising (i) at least one basic oxide selectedfrom-the group consisting of an alkali metal oxide and an alkaline earthmetal oxide and (ii) at least one acid oxide, and with at least oneoxidizer selected from the group consisting of a solid oxidizer, oxygengas, an oxygen-enriched gas and a mixture thereof, to form a double saltof said double oxide and said Mo oxides, and

discharging a slag containing said double salt.

2. The process of claim 1 wherein said Mocontaining alloy steel containsat least about 20 percent by weight of a component selected from thegroup consisting of Ni, Co and a mixture thereof.

3. The process of claim 1, wherein the basic oxide is selected from thegroup consisting of Na O, CaO, MgO, K 0, Li O, BeO, BaO, SrO, C5 0 andmixtures of two or more thereof.

4. The process of claim 1, wherein the acid oxide is selected from thegroup consisting of SiO Al O and mixtures thereof. H

5. The process of claim 1, wherein said Mo-alloy steel contains at leastabout 20 percent by weight of a component selected from the groupconsisting of Ni, Co

1. A REFINING PROCESS FOR REMOVING MO FROM A MOCONTAINING ALLOY STEELHAVING A HIGH CONTENT OF AT LEAST ONE OF NI AND CO, WHICH COMPRISES:SUBJECTING SAID MO-CONTAINING ALLOY STEEL TO OXIDATION MELTING REFININGAT A TEMPERATURE OF FROM ABOUT 1500*C. TO ABOUT 165*C. TO FORM APEROXIDIZED MOLTEN STEEL CONTAINING MO OXIDES AND HAVING THE FOLLOWINGAPPROXIMATE ELEMENTAL ANALYSIS IN PERCENT.
 2. The process of claim 1,wherein said Mo-containing alloy steel contains at least about 20percent by weight of a component selected from the group consisting ofNi, Co and a mixture thereof.
 3. The process of claim 1, wherein thebasic oxide is selected from the group consisting of Na2O, CaO, MgO,K2O, Li2O, BeO, BaO, SrO, Cs2O and mixtures of two or more thereof. 4.The process of claim 1, wherein the acid oxide is selected from thegroup consisting of SiO2, Al2O3 and mixtures thereof.
 5. The process ofclaim 1, wherein said Mo-alloy steel contains at least about 20 percentby weight of a component selected from the group consisting of Ni, Coand mixtures thereof.